Hagia Sophia

Hagia Sophia is a monumental building in Istanbul, Turkey, completed in 537 under the Byzantine emperor Justinian I as the principal cathedral of Constantinople. Its central dome, raised on pendentives above a square base, made it one of the largest interior spaces of its time and a landmark in the history of architecture. The name means "Holy Wisdom" in Greek. The building has been a Christian cathedral, an Islamic mosque, a secular museum, and, since 2020, again an active mosque, and each change has shaped how its art, architecture, and identity are read. It is part of the UNESCO World Heritage site Historic Areas of Istanbul, designated in 1985, and it is one of the most visited monuments in the world.

This entry first traces the site's earlier churches, the rebuilding after the Nika riots, and the design and engineering of the present structure, including the collapse of the first dome and its replacement. It then follows the building's major phases: its role in Byzantine religious and imperial life, the Latin occupation after 1204, the conversion to a mosque after 1453 under Ottoman rule, and the museum period that began in 1934. The entry then covers the 2020 change of status and the legal and diplomatic debate around it, the conservation and scholarly work on the building, and its lasting influence on architecture and cultural heritage.

Origins on the site and the Nika riots

The Hagia Sophia was the third church to stand on this ground in Constantinople, and the building that survives owes much of its form to the disaster that destroyed its immediate predecessor. The first church, the Megale Ekklesia ("Great Church"), was inaugurated on 15 February 360 under Constantius II, and it stood beside the imperial palace that was then under construction. The first church, known as the "Great Church" (Greek: Megálē Ekklēsíā; Latin: Magna Ecclesia), was inaugurated on 15 February 360 during the reign of Constantius II. It was built next to the imperial palace which was then under construction. Its wooden roof and basilica plan are known mainly from later descriptions, since little of the building has been excavated in detail. The first church was damaged in 404 during disturbances that followed the exile of the popular patriarch John Chrysostom, and it was rebuilt and enlarged.

The second church was commissioned by Theodosius II. Accounts differ on its date: some sources give 415 as the dedication year, while others give 405 as the inauguration. It was a basilica with richly carved decoration, and the name Hagia Sophia (Holy Wisdom) came into common use for the church around 430. Like its predecessor, it was not to last. Its roof was burned in the early fifth century, and in 532 the building was destroyed during the Nika riots.

The Nika riots began in January 532 as violence between the Blue and Green chariot-racing factions in the Hippodrome. The Riots began due to the growing political and social tensions in the capital between the two principal circus factions – the Blues and the Greens. The protest then grew into a wider revolt against taxation and Justinian's government. Fires spread through the city, and rioters continued to set fires throughout the city, one of which destroyed the Hagia Sophia (St. Sophia) church. After several senators proclaimed the former consul Hypatius as emperor, Justinian's generals Belisarius and Mundus trapped the crowd in the Hippodrome and suppressed the revolt. Estimates of the dead vary, but the figure of about 30,000 is widely cited. The destruction of the old church therefore came at the centre of a political crisis that had nearly ended Justinian's reign.

Justinian responded by rebuilding quickly and visibly. Within just five weeks of the riot the site had been cleared, building materials acquired, and, most remarkably, a revolutionary design adopted, according to one popular account, though this timeline is not confirmed by contemporary documents. The new church was built between 532 and 537, and the emperor inaugurated it on 27 December 537. The project served a clear political purpose. Justinian presented the building as proof that his regime had survived the revolt and was restoring order, and his goal of a new church that would be impervious to future fires and riots reflected that purpose. The rebuilding of the Hagia Irene, which was also burned in 532, belonged to the same programme of reconstruction.

The new church was assembled largely from materials that already existed in the empire. Marble and stone were drawn from quarries across the Mediterranean world. White-and-grey Proconnesian marble from the Sea of Marmara clad the walls and paved the floor, and this was combined with green verde antico from Thessaly, Egyptian porphyry, and other stones from North Africa and Phrygia. Some columns were reused from older monuments. Tradition holds that the green shafts came from the Temple of Artemis at Ephesus, though this attribution is difficult to verify. The workforce was also large. One tourism source gives a figure of about 10,000 workers and artisans, a number that cannot be checked against Byzantine records, so it should be treated as an estimate. The organisation of such a workforce, and the imperial resources that paid for it, reflect the reach of the late Roman state in the sixth century.

Design and the architects Anthemius and Isidore

Justinian gave the commission to two men whose reputations rested on learning as much as on building. Anthemius of Tralles, born around 474, came from a family of physicians and a lawyer, and one near-contemporary description calls him a professor of geometry at Constantinople. His earlier treatise on conic sections is often read as preparation for the church's complicated vaulting. He was commissioned with Isidore of Miletus shortly after the earlier church on the site burned down in 532 but died early on in the project. Isidore of Miletus is described as one of the two main Byzantine Greek mathematician, physicist and architects, and his familiarity with mechanics and mathematics is the reason the building's engineering is so often discussed. Neither man was a architect in the modern professional sense; their authority came from applied geometry and mechanics, which is why the church is usually read as a product of mathematical reasoning as much as of architectural tradition.

The plan is the first unusual feature. Robert Ousterhout describes it as combining two trends of early Christian design: a centralizing element inserted into a longitudinally-planned basilica, and a centrally planned church with a longitudinal axis added for liturgical purposes. Pendentives had been used before, but the scale was new: pendentives had been used in earlier buildings, but never at the scale and ambition of Hagia Sophia. The result is a long, processional nave that opens onto a domed core, a hybrid that later churches in the Byzantine world rarely attempted at this size.

The central dome is the structural centrepiece. Current figures give a diameter of 31.24 metres, with the crown rising 55.6 metres above the floor. The dome sits on four pendentives (curved triangular surfaces transitioning from a square base to a circular dome), supported by four massive piers concealed within the walls. Arches springing from the piers meet at the pendentives, so the load drops through them to the foundation. Because a dome pushes outward in every direction, the thrust has to be resisted on all sides: the lateral thrusts of the dome are countered on two sides by semidomes and on the other two by buttresses. The half-domes to the east and west therefore do structural work while also extending the central space into a single nave.

The walls were opened to reduce apparent mass. A ring of windows at the base of the dome lightens the springing line, which is where the load is heaviest, so that the masonry that holds the dome up simply vanishes, and the shallow golden canopy appears to hover. Windows in the walls above the galleries do the same work in daylight, obscuring the supports in the glare of daylight. Structurally, however, the forces are concentrated at a few points: the piers, the pendentive corners and the arches linking them. This system allowed the architects to dispense with rows of interior supports, though it made the performance of those few points critical, a vulnerability that became apparent when the first dome failed.

Dimensions vary between sources, which should be borne in mind. One engineering account gives the dome measured 120.5 ft in diameter, which is considerably larger than the 31 metres given in most architectural references. The current dome has also changed shape, and one source notes that due to several reconstructions and repairs over the centuries, the dome has lost its circular shape, and now measures 30.86 metres in diameter.

Structural failure and the second dome

The original dome lasted only about two decades. Earthquakes in 553 and 557 damaged the structure, and on 7 May 558 part of the central dome fell, destroying the ambon, altar and ciborium beneath it. Modern analyses usually attribute the failure to a combination of factors: the vault was very large for its time, its curvature was shallow, and it had been built quickly. A shallow dome throws more of its load outward, so the seismic shocks acted on a structure whose walls and arches already carried severe lateral thrust.

The contemporary record of the first dome's form is incomplete. Procopius, who wrote while the building was new, described it in general terms and did not give its profile. Agathias and John Malalas, writing about the reconstruction, indicate that the replacement was raised, and Malalas gives the original as roughly 20 feet lower. Paul the Silentiary, whose ekphrasis was written for the rededication in 563, describes the collapse in dramatic language rather than measurements. Because of this gap, the height of the first dome is reconstructed from indirect evidence. Some scholars have argued that the original was not a single shallow shell but a fenestrated cylindrical drum carrying a spherical segment. That reading is debated, and the question of what exactly fell remains open.

Justinian entrusted the repair to Isidore the Younger, nephew of the original architect Isidore of Miletus. According to Agathias, the surviving engineers examined the remains of the first design to determine what had failed and why. Isidore did not simply patch the damaged dome. He removed what remained of it and addressed the problem at the level of the arches. He strengthened the arches to the north and south and filled their spandrels with walls pierced by windows, and he raised the crown by roughly 6 metres. Accounts differ on the figure, with some giving about 10 metres, but the repaired dome was consecrated in 562 or 563.

The surviving dome is therefore a different form from Justinian's original. Its steeper profile is closer to a hemisphere, and the crown sits higher above the drum. The rebuild also changed the way the dome was supported and tied to the piers. What has been lost includes the original upper shell, its ribs and surfaces, and the exact geometry that Procopius and his contemporaries saw. The present dome is also a composite. Parts collapsed again in 989 and in 1346, and the repairs after those events, including the flying buttresses added in the mid-fourteenth century, mean that the shell and its supports now reflect several centuries of work. Its diameter is commonly given as about 31 metres, though figures vary slightly because of later deformation.

The failure and repair offer several lessons that architects and historians often cite. The first is the trade-off between curvature and thrust. A steeper dome reduces the outward force on the walls, but raising it adds height and weight, so Isidore paired the change with lighter construction and windows to limit the load. The second is that the vault cannot be understood apart from its supports. The arches, spandrels, piers and semi-domes form one load path, and the 558 failure showed that weakness in the arches could bring down the crown. Later proposals, such as a 1993 retrofit plan, focused on tying the main arches and semi-domes together so that they would act as one system during an earthquake. The third lesson concerns buttressing. External buttresses were added over the centuries, but historians have also noted that earlier interventions that removed or altered them created new stability problems. Finally, the building's survival, achieved without modern seismic codes or computer modelling, is frequently cited by engineers as evidence that continuous inspection and repair can matter as much as the original design. See structural engineering and architecture for the broader context, and Constantinople for the city's seismic setting.

Interior decoration and mosaics

Hagia Sophia's interior was conceived as a surface for light. Its upper vaults and galleries carried mosaic work, and the earliest of it was largely ornamental. In Justinian's time the vaults were covered with ornamental mosaics set in plain gold backgrounds, and some of these were later replaced with mosaics of saints, Christ and angels. Scenes from the first decoration included a Pentecost scene, with fiery tongues of light descending onto the Apostles, and gigantic cherubim and seraphim around a Christ Pantokrator set in a great circular medallion in the centre of the vault. The imperial programme is attested in the south gallery, where the imperial portrait mosaics sat beside the Deesis panel. At the height of the Byzantine Empire, the walls, vaults, columns and the dome were covered in gold-ground mosaics depicting Christ, the Virgin Mary, the saints, and the emperors and empresses who commissioned them. The marble revetments and the colonnades of the aisles, which framed these surfaces, are not described in the sources consulted here.

The surviving figurative work is mostly later. The figurative mosaics that once covered the cathedral were destroyed during the Iconoclasms that followed, and the oldest mosaics that exist today in Hagia Sophia date from the 10th through the 12th centuries. The most celebrated of these is the Deesis panel in the south gallery, showing Christ in the centre with his right hand blessing and his left hand holding the gospels, flanked by the Virgin Mary and Saint John the Baptist. Its date is disputed. One account places it in the late twelfth century, most likely from the reign of Manuel I Komnenos; another attributes it to the period after 1261, when Emperor Michael VIII Palaiologos, responsible for reclaiming the Byzantine capital, is likely responsible for installing a monumental new mosaic of the Deesis in the south gallery. Only part of the panel survives: a mosaic panel about four metres high, of which rather less than half survives. The seraphim were a second major group. The nave was dominated by four great six-winged mosaic seraphim in the pendentives, and two still survive. The mosaic seraphim in the western pendentives have vanished.

The mosaicists worked the gold ground to catch light. The gold tesserae that compose the background are arranged in a shell-like pattern and those in Christ's halo seem to swirl. Glass was used for the coloured tesserae, with gold-leaf sandwich cubes for the ground and silver-leaf cubes used sparingly in the highlights of the drapery. Because the tesserae were set at different angles, the surface shifted as the viewer moved while the faces remained stable. The liturgical effect depended on lamplight as much as on daylight. Semi-transparent gold glass is especially effective in reflecting lamp and candle light. Visitors recorded the effect in the nave: they remarked on how beautiful the masses of gold mosaic looked and how the sparkling light charged the air.

The later history of these surfaces is one of concealment and recovery. The figural mosaics had been hidden by whitewash and plaster for some 400 years. After the Ottoman conquest, the figurative work was covered, and out of respect for Muslim religious customs prohibiting the representation of humans, the figural mosaic panels were re-covered with plaster and painted. In 1847–49 the architects Gaspare and Giuseppe Fossati, working for the sultan, ordered the mosaics uncovered, and the two Swiss architects made careful notes of what they found before eventually recovering all the Christian decoration. Their work was not neutral, however. The paint they applied ended up destroying most of the Byzantine mosaics they uncovered. From 1931 the Byzantine Institute of America took over the work and was over an approximately 18-year period, the group removed the plaster that covered a significant number of the Byzantine era mosaics. Conservators who consolidated and cleaned the original mosaics were critical of some of the Fossati methods of conservation.

Byzantine religious and imperial role

For most of its history, Hagia Sophia was the principal church of Constantinople within the Byzantine liturgical tradition. From its dedication in 360 until 1453, Hagia Sophia served as the cathedral of Constantinople in the Byzantine liturgical tradition, except for the period 1204–1261. In practice this meant it was the seat of the Ecumenical Patriarch, the effective head of the Orthodox Church. It was also the principal setting for state ceremony. Coronations took place there, and imperial processions on major feast days linked the palace with the church, so that the building functioned as a stage for the emperor's public legitimacy as well as a place of worship.

The church's sacred prestige rested less on a single famous relic than on the wider network of relics and liturgical objects in the capital. Much of the most celebrated material was held in palace chapels such as the Pharos, whose collection included the Crown of Thorns and was described in detail by the official Mesarites in 1201. The sources on Hagia Sophia's own holdings are more fragmentary. Niketas Choniates reports that some of the cathedral's relics, such as a stone from the tomb of Jesus, the Milk of the Virgin Mary, the Shroud of Jesus, and the bones of many saints, were transferred to the West after 1204. The icon of the Hodegetria was also significant to the city's ritual life, and after the Crusaders had taken Constantinople in 1204, it had initially remained in Hagia Sophia. The building's name, the Holy Wisdom, refers not to a saint but to the second person of the Trinity, or Jesus Christ, which gave the church a theological identity distinct from the cults of individual holy figures.

The Fourth Crusade marked the sharpest break in this religious role. In 1204, Crusader armies captured and brutally sacked Constantinople, despite the city being Christian. The cathedral was ransacked for valuable materials like gold and marble, and the Latin conquerors then installed their own institutions. Baldwin of Flanders was crowned Emperor of the Romans there on 16 May 1204, following Byzantine practice. Under the agreement among the crusaders, the party that did not supply the emperor was entitled to appoint the clergy of the church, and the Venetian clergy chose Thomas Morosini as the first Latin patriarch. The Latin hierarchy remained until 1261, when Byzantine forces returned. The Byzantine restoration refurbished the church to Greek Orthodox tradition, and Michael VIII Palaiologos's workshops installed a large Deesis mosaic in the south gallery. Byzantine rule was restored, but the empire that returned was far weaker than its earlier form.

Contemporary and later writers treated the church as a measure of the empire's fortunes. Photios, in a sermon delivered in 867, spoke of the scars of those wounds left by iconoclasm, showing that the building's condition was already being read as a political and spiritual matter. Choniates' account of the sack and the removal of relics similarly frames the damage to the church as a catastrophe for the city's sacred order. Later Byzantine writers, and modern historians working from them, therefore tend to present Hagia Sophia as the embodiment of imperial and religious identity, with its losses and recoveries serving as markers of the state's health.

Ottoman mosque and architectural additions

Conversion and the first alterations

Sultan Mehmed II designated the previously Christian church a mosque shortly after he conquered the city in 1453. Rather than demolishing the building, the conqueror placed it under waqf status, so that endowment revenue would fund its upkeep. He placed it under waqf status. This meant revenue funded its maintenance forever. The first alterations were modest in number. During Mehmed's rule, a wooden minaret (no longer standing), a mihrab (niche positioned in the direction of Mecca), a minbar (pulpit), a madrasah (school), and a grand chandelier were added. The mihrab was set about ten degrees off the building's main axis so that it faced Mecca, which was the orientation Islamic practice required. Later changes followed the first ones, since bringing the structure in line with the Islamic tradition called for a series of other modifications, not all of which were undertaken during his reign.

Minarets, buttresses and funerary buildings

The building eventually acquired four minarets. These were put up by different rulers over roughly a century, and they are the most visible marker of the mosque's exterior. Added progressively by different sultans between 1453-1574 is how one guide summarises their dating. The structural history was equally important. Buttresses had already been added to the church before 1453: flying buttresses were added to the northwest façade as early as the 9th or 10th century, supplemented by the construction of buttresses to the south and southeast by Andronicus II in early 13th century, amended by the Ottomans. The Ottoman architect Mimar Sinan later worked on the fabric directly, and Mimar Sinan carried out major structural interventions and strengthening works.

Successive rulers also turned the surrounding precinct into an imperial religious complex. Successive sultans added buttresses, tombs, a library, fountain, school and other buildings that turned Hagia Sophia into an imperial religious complex. The former baptistery was converted into a tomb in 1639, and several sultans were buried in the adjoining structures, with the grave of Mustafa I among the best known. The complex also included a fountain and a library, reflecting the charitable and educational functions common to Ottoman külliye complexes.

Calligraphic medallions and the covered mosaics

Among the most distinctive Ottoman additions are the large calligraphic roundels hung in the nave. Eight massive medallions hung on columns in the nave bear Arabic calligraphy with the names of Allah, the Prophet Muhammad, the first four caliphs of the Rashidun Caliphate, and the Prophet's two grandsons. The calligraphy is attributed to Kazasker Mustafa Izzet Efendi, and the same calligrapher worked on the medallion at the top of the dome, which quotes the Light Verse (24:35), inscribed by Mustafa Izzet Efendi during the Fossati restoration.

The treatment of the Byzantine figural decoration was more selective than is often assumed. Islamic tradition excluded figural imagery from sacred space, and the Muslim ban on imagery resembled that of the two iconoclastic periods and they covered many of the Hagia Sophia's mosaics with plaster. Yet the covering was not uniform. Detailed drawings made of Hagia Sophia during its phase as a Muslim space of worship have shown that practically none of the Christian religious imagery was covered during a majority of Ottoman reign. Seraphim in the pendentives were among the figures that were plastered over at some point during Ottoman rule. Overall, icons were covered, not destroyed.

Dual identity and the Ottoman mosque tradition

The building's mixed character was recognised even by its Ottoman patrons. Mehmed II's own endowment deed described the church as an exquisitely decorated church, a phrase that preserved its Christian origin in the legal record. The Ottoman interventions did not produce a clean replacement of the earlier layer. They introduced a mihrab, minbar, calligraphy, lighting, royal spaces, educational institutions and structural reinforcement while retaining the great sixth-century central volume.

The building also became a model for later imperial mosques. Its architectural style was emulated by Ottoman mosques a thousand years later. The first major imperial mosque in the city, the Fatih Mosque completed in 1470, demonstrated an increasing influence of the ancient Hagia Sophia on Ottoman architects while also setting a precedent for vast külliye complexes with a highly organized site plan. The lineage continued into the sixteenth century. Other mosques that drew on the design include the Şehzade, Süleymaniye and Rüstem Pasha mosques in Istanbul. In the Bayezid II Mosque, a much more sophisticated "cascade of domes" effect for the building's exterior profile is read as reflecting influence from Hagia Sophia and the Fatih Mosque.

Museum period and modern conservation (1934–2020)

From mosque to museum

The change of status began in August 1934, when the education minister wrote to the prime minister's office about a plan to turn the mosque into a museum. The prime ministry immediately created a commission and drafted a to-do list within two days. The cabinet's ruling of 24 November 1934 formalised the change. The government presented it as part of Atatürk's wider secularising reforms, and the monument was described as shared cultural heritage rather than a religious institution. This decision was part of Atatürk's broader secularization reforms and aimed to present the building as a shared cultural heritage site rather than a religious institution.

The decree remains a point of contention. Its signature reads "K. Ataturk," although the founder did not use that surname on the date, which has led many to suspect forgery. The signature on the decree dated November 24, 1934 spells K. Ataturk. However, it is well-known that the founder of Turkey and first president had not yet adopted the surname Ataturk on that date, and was back then simply known as Gazi Mustafa Kemal. This has made many believe that Mustafa Kemal Ataturk's signature was forged. Administratively, the site moved from the foundations directorate to the museums directorate. In a protocol meeting between the Mayor of Istanbul, the Foundations Director and the Museums General Manager, the mosque was transferred from the Foundations department to the Museums department. The building was closed for repairs in December 1934 and reopened in February 1935. The monument, which had been closed on 9 December 1934 due to repairs, was opened to visitors on 1 February 1935 with a new identity. Atatürk was among the first to visit. Atatürk was among the new museum's earliest visitors, travelling especially from Ankara in February 1935.

Uncovering the mosaics

The museum period is closely tied to the recovery of the mosaics, which had been plastered over during the Ottoman era. Earlier, in 1847–49, the Fossati brothers had exposed some figural mosaics and then covered them again. When the Fossati brothers restored the building in 1847–49, they recorded mosaics they then covered again — and their drawings are, for some images, our only record. In the museum period, the work was given to the Byzantine Institute of America, which was founded by the American scholar Thomas Whittemore. In December 1931, Thomas Whittemore and his newly founded Byzantine Institute of America were authorized by the Turkish government to lead the restoration and conservation efforts for the Hagia Sophia interior mosaics. Atatürk reportedly favoured revealing the mosaics. It was Atatürk's belief that the mosaics should be revealed, and the work was entrusted to Thomas Whittemore and the Byzantine Institute of America, which he directed. The Byzantine Institute's work was long: The arduous and painstaking work of restoring the historic Byzantine mosaics began in 1932 continued for about 18 years, long after the cathedral reopened as a museum.

Not all of the recovered imagery survives in complete form. What you see is original Byzantine work, cleaned and uncovered by the Institute and documented as they went — though some of it is fragmentary, with portions lost over the centuries. The Deesis is the clearest case: its lower half is gone, leaving a genuine thirteenth-century masterpiece that simply survives in part. Historians have also argued that the restorations did not simply return the building to an earlier state. That restoration did not, of course, return the building to its prior life or lives. Like all such projects, it instead gave it a new and different life, helping the church/mosque to become a monument.

Conservation continued after the Institute's work. This, the most recent of many efforts to restore and preserve Hagia Sophia, began in 1992. Conservators working on scaffolding have examined the mosaic tesserae, which are small glass cubes that often have gold or silver leaf beneath a clear layer of glass. Today, conservators on the scaffolding are busily examining the tesserae, the small cubes making up the mosaic, each one cut from a layer of glass on which leaves of gold or silver were placed, covered by a thin piece of clear glass, then fused together in a kiln. They are checking each of the millions of tesserae, cleaning and consolidating them.

International recognition

In 1985 the building entered the World Heritage List as part of a larger group. These areas were added to the UNESCO World Heritage List in 1985. The inscribed property, the Historic Areas of Istanbul, is located in the Fatih district and includes other major monuments of the city. The inscription, which placed the building within a wider urban heritage framework, reflected the international view of the monument's value as part of the city's cultural heritage.

Visitors and debates over identity

Visitor numbers have been very large. Hagia Sophia, one of the most prominent monuments taking place in Istanbul, Turkey, hosts millions of visitors every year. The museum displays juxtaposed Byzantine and Islamic elements. The building's dual heritage - both Byzantine Christian and Ottoman Islamic - was celebrated and preserved, with mosaics displayed alongside Islamic calligraphy. This arrangement made the building a symbol of the Republic's secular identity, but it was also read by critics as a top-down decision. One commentator noted that the public and newspapers weren't able to raise their voices, and the state, without questioning anything, used all its resources to make it happen. An academic analysis of the decision called it undeniably an administrative decision. The status of the museum was later challenged through the courts, which is covered in the next section of this entry, on the Association for the Service of Historical Foundations and the Environment filed a lawsuit with the Council of State seeking to annul the 1934 Cabinet decision. The museum's place in judicial review debates has made it a focus of wider discussions about culture and religion in modern Turkey.

2020 reconversion and the legal and diplomatic debate

The legal basis for the 2020 change was a ruling by the Tenth Chamber of Turkey's Council of State, the highest administrative court. The case had been brought in 2016 by an association concerned with historic foundations and the environment, and it asked for the Cabinet decision of November 1934 to be annulled. The chamber's reasoning treated the building as property of the waqf (charitable endowment) that Mehmed II's foundation had established, and held that under the law in force when the endowment was created, its status could not be altered by administrative decision. Critics have argued that the judgment was less an adjudication than a reflection of executive preferences, and that the references to European human rights case law were weak.

The presidential decree followed within days. President Recep Tayyip Erdoğan signed it on 10 July 2020, transferring management of the building from the Ministry of Culture to the Presidency of Religious Affairs (Diyanet) and approving its use for worship. The mosque was officially reopened for Friday prayer on 24 July 2020, the first Muslim prayers there in roughly 86 years. The government presented the step as correcting a historical wrong committed under Atatürk and as a restoration of national sovereignty. Erdoğan described foreign objections as a direct challenge to Turkish sovereignty.

International and religious reactions were largely critical. The Ecumenical Patriarch Bartholomew I warned before the decision that it would disappoint millions of Christians and could fracture relations between East and West. The Moscow Patriarchate's external relations department, through Metropolitan Hilarion, stressed that the church was a symbol of Byzantium and of Orthodoxy for Orthodox believers worldwide. The Cypriot president, Nicos Anastasiades, called the move a historical appropriation and desecration of a World Heritage monument. The United States Secretary of State urged Turkey to keep the building a museum as a sign of pluralism. In September 2020 the Greek Orthodox Archdiocese of America petitioned United Nations experts, accusing Turkey of deliberately erasing Orthodox Christian heritage.

UNESCO expressed concern and asked the Turkish authorities to open a dialogue to avoid a step back from the site's universal value, noting that the World Heritage Committee would review its preservation. Some commentators in Turkey, meanwhile, were sharply opposed to the reversal, and secular circles protested the decision. Accounts also differ on the exact date of the court's ruling: some give 2 July, when the decision was reported, and others give 10 July, the date the chamber's judgment was recorded.

Current visitor arrangements

As of the most recent guides, the site functions as an active mosque, and its arrangements divide worshippers from tourists. Worshippers enter the ground-floor prayer area free of charge through the main gate on the Sultanahmet Square side. Since 15 January 2024, non-Muslim visitors have paid an admission fee and use a separate entrance on the northeast side, which leads to the upper galleries where the Byzantine mosaics are displayed. The tourist route closes around each of the five daily prayers, and the longest closure is on Fridays around midday. Published closure times differ between sources, and they shift with the seasons and the daily prayer schedule. During prayers the Byzantine mosaics are covered with curtains and uncovered afterwards.

Research, dating, and conservation challenges

Knowledge of the building's first form depends on a small set of literary sources, and the most important of them is also the hardest to interpret. The text about Hagia Sophia is the only surviving historical source for the original Justinianic edifice before the collapse of its first dome in 558. Procopius wrote in the rhetorical style of ekphrasis, so his descriptions of architectural features are open to competing readings. Procopius's accounts provide essential insights, yet they are often misinterpreted, obscuring true architectural features. For example, medieval illustrations depict a non-existent drum, complicating our understanding of the dome's original design.

Agathias, writing after the collapse, supplies a different kind of evidence. He describes the rebuilding and its materials, noting that the church was built of baked brick and mortar with iron binding and no timber. When, as a result of the earthquake, the church had lost the central part of the roof, the emperor repaired it in a more secure fashion and raised it to a greater height. However, Agathias is silent on the subject of a drum, which means his account cannot settle the question of the first vault's profile. The chronicler Theophanes adds the detail that the collapse happened during repairs, and he blames the engineers for tunnelling the piers instead of securing the support from below. Modern historians treat that charge with caution because it reflects the attitudes of the sources rather than measured evidence.

The form of the first dome

The central debate concerns the height and profile of the 537 dome. One reading, associated with Rabun Taylor, proposes that the original vault had an upper dome constituting a spherical segment and a fenestrated, cylindrical lower drum. A later study that combined structural analysis with the literary evidence found that a finite element model analysis supports a fenestrated drum and segmental dome design for the first dome. Estimates of the height difference also vary. Taylor argued for a difference of about ten feet, while Mainstone's reconstruction implied roughly twenty feet, a gap that depends on how large the drum was taken to be.

Other reconstructions reject the drum entirely. The interior of the first dome may have been profiled like the pendentives, creating a "pendentive dome" with an interior radius of about 23 metres. Because no physical trace of the first dome survives, each model depends on assumptions about the lost geometry, and none has been confirmed by excavation.

Earthquakes, repairs, and monitoring

Earthquakes have been the building's most persistent structural threat. The first central dome fell in 558 after being subjected to two major earthquakes: the first of these in August 553, and the second in December 557. Dates given in other sources differ slightly, so chronologies of the sequence should be read with that uncertainty in mind. After 558, the church suffered further partial damage. In 1509, 1556, 1754 and 1766 earthquakes partial damage of the dome and in 1894, light damage at the dome of the structure were also recorded. In the 16th century, the Ottoman chief architect Sinan fortified the structure with external buttresses during the reign of Sultan Selim II.

Modern studies have identified the weak points. One analysis argues that the detachment of the eastern and western semi-domes from the eastern and western main arches constitute one of the most important collapse mechanisms in a large earthquake. Monitoring began early: Hagia Sophia has been monitored with a structural health monitoring system since 1991. The system was upgraded in 2008 and has since recorded over 100 seismic events. In 2025, a retrofit was announced that would cover the main dome and half-domes while their coverings were removed and the structure reinforced. Conservation specialists have also noted that the building's own materials matter: the mortar of the structure has been measured with a maximum tensile strength of 3.5 MPa, affecting its stability.

Open questions

Several basic questions remain unresolved. The construction timeline is one. Official and scholarly accounts give a date of completion in 537, but estimates of the building period vary: one study gives five years and ten months after construction began, while popular accounts use a round figure of six years. The workforce is another open question. The sources examined here do not provide a reliable count or breakdown of labour, so the organization of the site cannot be reconstructed with confidence. The exact form of the lost first dome is the third. Each proposed reconstruction rests on a different reading of Procopius and a different treatment of the drum, the profile, and the ribs.

Conservation also raises its own problems. Recent restoration has uncovered hidden features, such as ancient mosaics and depictions of angels, beneath previous layers of plaster. Each intervention thus adds new evidence while also changing the material that future researchers will study.

Architectural and cultural legacy

Influence on Byzantine and Russian churches

The dome was copied and adapted across the Orthodox world, though the extent of direct borrowing is debated. Saint Sophia in Kyiv is the best-known case. One line of scholarship holds that its forms were Byzantine types built by Byzantine-trained masters, while another argues that the Kyiv church borrowed little from Constantinople beyond its name and some general features. The Kyiv church also became a model in its own right, lending its name and plan to the Sophia churches of Novgorod (1046) and Polotsk (1048–1052). In the West, St Mark's Basilica in Venice is often described as modeled on Hagia Sophia and on the Church of the Holy Apostles in Constantinople, and its five domes rise on pendentives, a feature that sources credit to Hagia Sophia. Its exterior was also decorated with marble spolia brought from Constantinople.

Ottoman imperial mosque design

The Ottoman relationship with the building was one of close emulation. The Fatih Mosque, completed in 1470, was the first imperial mosque in the city and already showed a growing debt to Hagia Sophia, while setting a precedent for large complexes (külliye) with organized plans. The architect Mimar Sinan produced the most direct descendants: the Süleymaniye Mosque, built in the 1550s, and the Kılıç Ali Paşa Mosque (1580) reproduce the building's plan and structure closely. Sinan was not a mere copyist, however. His Selimiye Mosque in Edirne (1569–1575) has a dome of nearly the same diameter but follows a noticeably different type. Ottoman builders also learned from the original's weaknesses. The dome's structural problems were attributed largely to the use of only two semi-domes and to the sheer monumentality of the dome, so later Ottoman mosques were often smaller or more stable. The principle of a large central dome, as opposed to the Hagia Sophia's specific solution, remained the reference point for Turkish mosque design into the modern period.

Historiography and Western perception

Western appreciation of the building changed considerably over the nineteenth century. Earlier Enlightenment writers had generally regarded it unfavourably, and interest rose after the Fossati brothers' restoration. Their 1852 London portfolio of twenty-five lithographs depicted the building as a working mosque, and a critical review argues that this imagery gave the church much of its "Oriental" appeal in Western eyes. Robert S. Nelson's study of Hagia Sophia from 1850 to 1950 interprets its cupola as the supreme expression of Byzantine achievement, a view that helped establish the dome as a model for Western architects. Nineteenth-century scholarship also revived interest in the mosaics, which had been plastered over for centuries, and Byzantine art in general became a field of academic study built partly around this monument.

Symbol of Istanbul and a case of reinterpretation

Few buildings illustrate the reinterpretation of religious space as clearly. The Hagia Sophia has been an Eastern Orthodox church (537–1204), a Roman Catholic cathedral (1204–1261), an Eastern Orthodox church again (1261–1453), a mosque (1453–1935), a museum (1935–2020), and a mosque once more from 2020. Its status within the UNESCO-listed historic areas of Istanbul ties it to the city's identity as a whole. Comparable buildings show similar shifts. The Hagia Sophia in Trabzon was converted into a museum in 1964 and returned to use as a mosque in 2013, while the Hagia Sophia at Mystras reverted to Christian use after Greek independence in the early nineteenth century. Scholars studying such sites emphasize that different communities have adopted, adapted, or dismissed the same architectural elements according to their own priorities.

Heritage management and contested monuments

The building is frequently cited in discussions of how to manage multilayered monuments, where Byzantine, Ottoman, and modern phases coexist in the same fabric. Heritage specialists debate whether later interventions, such as plaster over mosaics, the addition of minarets, or the restoration of figurative imagery, should be treated as part of the monument's significance or as changes to be reversed. The case has been used to examine how international designations like World Heritage status interact with national policy and religious claims, and how the physical structure can carry several contested identities at once.

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